The present invention is a device for high velocity impingement mixing and dispensing of two or more liquid polymeric reactants, for example polyurethane, in which the mixed reactants are dispensed into a mold cavity or onto a surface.
In high pressure impingement mixing, two or more liquid polymeric reactants are directed, from opposite directions, into a common mixing chamber so that the reactants are mixed together to achieve a uniform reaction. The mixed reactants are dispensed from the mixing chamber into a mold cavity or onto a surface. Typical mixing devices of this type are shown and described in U.S. Pat. No. 3,706,515 and U.S. Pat. No. 4,239,732.
In one type of application, mixing heads of this type are used for reaction injection molding (RIM). In RIM applications, the mixing head is installed as part of the closed mold, for example by being mounted in one of the mold dies. The mixed materials are dispensed into the mold cavity using aftermixer devices, runners, and film gates.
Mixing heads of the type shown in the aforementioned patents may also be used for open pour applications, e.g. where the mixed materials are dispensed into open molds which are closed after dispensing the reactants. However, in open pour applications, the use of known high pressure impingement mixing apparatus is limited to the processing of only certain chemicals. Due to the absence of aftermixer devices (which remix the reactants) and other RIM apparatus, known high pressure apparatus is limited to chemicals which can be mixed in a very short period of time and limited to chemicals in which the mixture, which is essentially an emulsion, is of the type that remains stable until the viscosity of the mixture increases, because of progressing polymerization and creaming, to a degree sufficient to prevent the phase separation of the reactants.
In view of the shortcomings of known high pressure impingement mixing apparatus, it has not been possible to process on such equipment certain eleastomeric type materials, for example, materials used for the production of automobile fascia parts, or furniture parts, unless the high pressure mixing head was used in conjunction with well designed aftermixer devices and gate systems integrated into the molds. Similarly, in open mold applications, despite the progress in high pressure impingement mixing and new developments in chemicals, it has not been possible to produce products such as polyurethane shoe soles, using high pressure equipment, of the same, good quality as achieved using low pressure metering and mixing systems.
The same is true for the production of parts produced from self-skinning foam materials, where the skin represents the final surface of the part. Typical parts of this kind are arm rests for cars, aircraft or furniture, as well as headrests and steering wheels. Irregularities in the skin surface due to poor or incomplete mixing, or separation effects, and lead-lag spots in the surface renders the part useless. Until now, this type of material could only be processed on low pressure machines or processed with high pressure impingement equipment using specialized molds, that is, molds fitted with appropriate aftermixer devices and gate systems.
The ability to use high pressure impingement devices in applications where it is presently only possible to use low pressure systems, is highly desirable. High pressure impingement devices have mechanical clean out of the reactants in the mixing chamber, which provides considerable savings, relative to low pressure systems, due to the elimination of solvent flush required for low pressure machines, as well as a drastic reduction of waste material. The environmental hazards and problems connected with the use of solvents, for example, methylene chloride, utilized in low pressure apparatus would also be eliminated.
The substitution of high pressure mixing apparatus, if the mixed product were of a quality equivalent to the low pressure systems, could also readily be effected. Molds and mold clamps presently in use for low pressure systems could be retained, without modification, for the high pressure impingement mixing. Also, in high pressure mixing, if apparatus were available which would not, for effective mixing and formation of the end products, require the customary aftermixer and film gates, replacement molds could be built cheaper than in the case of presently known RIM processes, where such aftermixer and film gates have to be integrated into the mold.
In the past, several approaches have been taken in an effort to expand the applicability of high pressure impingement mixing systems. Such designs were directed to modifying the flow conditions of the mixture at the mixing head outlet, which in high pressure equipment is characteristically turbulent, to achieve laminar, non-splashing flow at the dispense outlet of the mixing head for open pour applications. One example of such a device is shown in my prior U.S. Pat. No. 4,175,874. Krauss Maffei and Cannon market a laminar dispense device in the form of an L-shaped mixing head. In such devices, the reactants are mixed in a mixing chamber having relatively small dimension, and the mixture thereafter flows into a larger dispense cylinder arranged at a right angle to the mixing chamber to effect a discontinuity in the direction of flow. Bayer-Hennecke currently markets a mixing head in which reactants are directed at one another from opposite sides of the dispense chamber, where they mix. A flow restriction is interposed between the mixing portion and the outlet of the dispense chamber so as to achieve the flow discontinuity of the turbulent flowing mixture and effect laminar flow at the outlet. While the achievement of laminar flow does improve the ability to use high pressure mixing systems in open pour applications, such presently known devices still do not produce satisfactory results when used in the applications described above.